The present invention relates to a device for recording information on a disk such as an optical disk in a concentric or spiral manner.
Recently, there has been developed an image information storing and retrieving device. In the device image information such as documents prepared in a mass are photoelectrically converted by a two-dimensional scanning. These photoelectrically converted image information are stored in or retrieved from an image information storage device in order to reproduce and output them as hard or soft copies. An optical disk device has been developed for an image information storage device adopted in such an image information storing/retrieving device.
In such an optical disk device, documents to be stored are scanned by a two-dimensional scanning device with a scanning laser beam. Video signals from the two-dimensional scanning are frequency modulated to produce FM signals, by which laser beam for storing information is turned on and off to produce modulated beam. By this modulated beam, the spinning optical disk is scanned on its metal coated surface and along its spiral track. As a result, the metal coated surface is melted and deformed in accordance with the modulated beam thereby forming a string of pits. Image information are thus recorded as a spiral track-shaped string of pits.
When video signals thus recorded are to be reproduced, the recorded track is scanned by laser beam while the disk is spinning. Modulated reflected light is detected from the pits on the recorded track and is photoelectrically converted to FM signals, which are demodulated to video signals, from which image information are reproduced. When recording information using such recording method as described above, linear velocity is different between inner and outer tracks of the optical disk. When recording is carried out at the innermost track of the optical disk by means of record timing signals having such frequency as keeping the pit distance smallest, therefore, the pit distance becomes larger at the outermost track thereof to lower its recording density. When the smallest pit distance is l at the innermost track of an optical disk 1 as shown in FIG. 1, for example, the pit distance becomes largest L at the outermost track thereof. To overcome the above drawback, there has been provided a method for making recording frequency constant and changing the spinning frequency of the disk, so that linear velocity may be kept constant at inner and outer tracks of the disk to achieve recording at the smallest pit distance along all the tracks. According to this method, however, the spinning frequency of the optical disk must be changed proportional to its radial position, thus causing the motor control circuit for controlling the optical disk driving motor to be complicated and taking a long time until the spinning frequency of the optical disk is settled.